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 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
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package java.util;

/**
 * An iterator for lists that allows the programmer
 * to traverse the list in either direction, modify
 * the list during iteration, and obtain the iterator's
 * current position in the list. A {@code ListIterator}
 * has no current element; its <I>cursor position</I> always
 * lies between the element that would be returned by a call
 * to {@code previous()} and the element that would be
 * returned by a call to {@code next()}.
 * An iterator for a list of length {@code n} has {@code n+1} possible
 * cursor positions, as illustrated by the carets ({@code ^}) below:
 * <PRE>
 * Element(0)   Element(1)   Element(2)   ... Element(n-1)
 * cursor positions:  ^            ^            ^            ^                  ^
 * </PRE>
 * Note that the {@link #remove} and {@link #set(Object)} methods are
 * <i>not</i> defined in terms of the cursor position;  they are defined to
 * operate on the last element returned by a call to {@link #next} or
 * {@link #previous()}.
 *
 * <p>This interface is a member of the
 * <a href="{@docRoot}/../technotes/guides/collections/index.html">
 * Java Collections Framework</a>.
 *
 * @author Josh Bloch
 * @see Collection
 * @see List
 * @see Iterator
 * @see Enumeration
 * @see List#listIterator()
 * @since 1.2
 */
public interface ListIterator<E> extends Iterator<E> {
  // Query Operations

  /**
   * Returns {@code true} if this list iterator has more elements when
   * traversing the list in the forward direction. (In other words,
   * returns {@code true} if {@link #next} would return an element rather
   * than throwing an exception.)
   *
   * @return {@code true} if the list iterator has more elements when traversing the list in the
   * forward direction
   */
  boolean hasNext();

  /**
   * Returns the next element in the list and advances the cursor position.
   * This method may be called repeatedly to iterate through the list,
   * or intermixed with calls to {@link #previous} to go back and forth.
   * (Note that alternating calls to {@code next} and {@code previous}
   * will return the same element repeatedly.)
   *
   * @return the next element in the list
   * @throws NoSuchElementException if the iteration has no next element
   */
  E next();

  /**
   * Returns {@code true} if this list iterator has more elements when
   * traversing the list in the reverse direction.  (In other words,
   * returns {@code true} if {@link #previous} would return an element
   * rather than throwing an exception.)
   *
   * @return {@code true} if the list iterator has more elements when traversing the list in the
   * reverse direction
   */
  boolean hasPrevious();

  /**
   * Returns the previous element in the list and moves the cursor
   * position backwards.  This method may be called repeatedly to
   * iterate through the list backwards, or intermixed with calls to
   * {@link #next} to go back and forth.  (Note that alternating calls
   * to {@code next} and {@code previous} will return the same
   * element repeatedly.)
   *
   * @return the previous element in the list
   * @throws NoSuchElementException if the iteration has no previous element
   */
  E previous();

  /**
   * Returns the index of the element that would be returned by a
   * subsequent call to {@link #next}. (Returns list size if the list
   * iterator is at the end of the list.)
   *
   * @return the index of the element that would be returned by a subsequent call to {@code next},
   * or list size if the list iterator is at the end of the list
   */
  int nextIndex();

  /**
   * Returns the index of the element that would be returned by a
   * subsequent call to {@link #previous}. (Returns -1 if the list
   * iterator is at the beginning of the list.)
   *
   * @return the index of the element that would be returned by a subsequent call to {@code
   * previous}, or -1 if the list iterator is at the beginning of the list
   */
  int previousIndex();

  // Modification Operations

  /**
   * Removes from the list the last element that was returned by {@link
   * #next} or {@link #previous} (optional operation).  This call can
   * only be made once per call to {@code next} or {@code previous}.
   * It can be made only if {@link #add} has not been
   * called after the last call to {@code next} or {@code previous}.
   *
   * @throws UnsupportedOperationException if the {@code remove} operation is not supported by this
   * list iterator
   * @throws IllegalStateException if neither {@code next} nor {@code previous} have been called, or
   * {@code remove} or {@code add} have been called after the last call to {@code next} or {@code
   * previous}
   */
  void remove();

  /**
   * Replaces the last element returned by {@link #next} or
   * {@link #previous} with the specified element (optional operation).
   * This call can be made only if neither {@link #remove} nor {@link
   * #add} have been called after the last call to {@code next} or
   * {@code previous}.
   *
   * @param e the element with which to replace the last element returned by {@code next} or {@code
   * previous}
   * @throws UnsupportedOperationException if the {@code set} operation is not supported by this
   * list iterator
   * @throws ClassCastException if the class of the specified element prevents it from being added
   * to this list
   * @throws IllegalArgumentException if some aspect of the specified element prevents it from being
   * added to this list
   * @throws IllegalStateException if neither {@code next} nor {@code previous} have been called, or
   * {@code remove} or {@code add} have been called after the last call to {@code next} or {@code
   * previous}
   */
  void set(E e);

  /**
   * Inserts the specified element into the list (optional operation).
   * The element is inserted immediately before the element that
   * would be returned by {@link #next}, if any, and after the element
   * that would be returned by {@link #previous}, if any.  (If the
   * list contains no elements, the new element becomes the sole element
   * on the list.)  The new element is inserted before the implicit
   * cursor: a subsequent call to {@code next} would be unaffected, and a
   * subsequent call to {@code previous} would return the new element.
   * (This call increases by one the value that would be returned by a
   * call to {@code nextIndex} or {@code previousIndex}.)
   *
   * @param e the element to insert
   * @throws UnsupportedOperationException if the {@code add} method is not supported by this list
   * iterator
   * @throws ClassCastException if the class of the specified element prevents it from being added
   * to this list
   * @throws IllegalArgumentException if some aspect of this element prevents it from being added to
   * this list
   */
  void add(E e);
}
